What is causing this woman's large thyroid swelling?

This 81-year-old lady was in reasonable health, other than a painful left leg. She had fractured her femur two years previously and it hadn't healed despite an intramedullary nail fixation. When she was in her early 40s she had a right hemithyroidectomy for what appeared to be an overactive nodule. She was not a regular attender. A recent TFT was normal.

Her dentist had passed her onto the maxillofacial surgeons for an upper molar removal. I received a letter saying they had incidentally picked up a thyroid lump and asked me to refer to ENT, which I duly did. Helpfully, the maxfax registrar had ordered an ultrasound of the patient's neck. It showed a heterogeneous thyroid swelling of at least 8cm by 7cm on the right lobe and a suspicious 3cm nodule on the left lobe.

Differential diagnoses

• Simple goitre

• Multinodular goitre

• Thyroid malignancy

Simple diffuse swelling of the thyroid is reasonably common and harmless. It is often idiopathic or may be related to hypothyroidism. But the ultrasound did not support this. A multinodular goitre was a possibility, but we needed to rule out thyroid cancer so she underwent a fine needle aspiration.

Cytology showed follicular cells only, with no evidence of malignancy. ENT saw the patient a few months later and put her on six-monthly reviews – which proved to be a mistake.

The hidden clue

The leg fracture was still not healing and looked suspicious on the latest X-ray. She was referred to a tertiary centre and underwent an MRI, ultrasound and biopsy of the callus on the fracture site.

Getting on the right track

Remarkably, this showed metastatic follicular carcinoma of the thyroid. Thyroid cancer is rare, with an incidence of about 4 per 100,000 per year. The two most common are papillary adenocarcinoma (80% of thyroid cancers) and follicular (10%). Follicular adenocarcinoma affects women more than men, in a 3:1 ratio. It is angioinvasive to the lungs and bones in over half of cases, which may be the first presentation – exactly the case in this lady.

This case shows how, even when presented with a neck lump, we must always look at the patient as a whole.